Association Between Soil Lead and Blood Lead - Evidence

Mark Laidlaw, PhD

New York Times Article - 1925

In 1925, The New York Times Published the following words of Dr. Yandell Henderson, Professor of Applied Physiology at Yale University:  the breathing day by day of fine lead dust from automobiles using leaded gasoline will produce chronic lead poisoning on a large scale in the population of cities  and would cause  vast number of the population to suffer from slow lead poisoning . He stated that  This is probably the greatest single question in the field of public health that has ever faced the American public . Furthermore, he stated that  It is the question whether scientific experts are to be consulted, and the action of the Government guided by their advice; or whether, on the contrary, commercial interests are to be allowed to subordinate every other consideration to that of profit".

Caltech Professor Clair Patterson stated the following in 1980: Sometime in the near future it probably will be shown that the older urban areas of the United States have been rendered more or less uninhabitable by the millions of tons of poisonous industrial Pb residues that have accumulated in cities during the past century Extrapolating from present information, probably it will be shown in the future that average American adults experience a variety of significant physiological and intellectual dysfunctions caused by long-term chronic lead insult to their bodies and minds which results from excess exposures to industrial lead that are five hundred-fold above natural levels of lead exposure, and that such dysfunctions on this massive scale may have significantly influenced the course of American history. (NRC, 1980; see p. 265-349). This pivotal and controversial statement of Clair Pattersons provided inspiration for this website.

The three main sources of lead exposure in urban environments are:

1) Soil (from leaded gasoline, exterior lead paint and lead smelters);
2) House Dust (from lead in soil and interior paint particles);
3) Water (from lead water lines)

This website focuses mainly on soil lead and does not thoroughly discuss the lead paint and water sources.

The lead emitted from gasoline (see line in blue) in high traffic inner city areas between the 1920's and 1980's (in the US) was deposited and incorporated within the top 5-10 centimetres of the surrounding soils. We now know that the lead in these soils can become resuspended into the air where it migrates into homes. People and pets also track the lead contaminated soil into homes. Children and adults are then poisoned. This, and in certain cases exposure to flaking lead paint and lead from lead water pipes, has resulted in epidemics of lead poisoning in large parts of some inner-city areas. This is a global phenomenon and will continue until lead in soil dust in urban areas is isolated.

An example of the lead poisoning epidemic - Detroit, Michigan

2001

2012

The above map shows the number of lead poisoning incidences per address/home in the City of Detroit. The yellow dots show that there are 4,610 homes in the city with two occurrences per home; these are the most frequent. However, the blue dots, which show three to five or six to nine occurrences per home, cover more of the map because of the higher number of people affected. There was one home in the southwest portion of the city that had 17 lead poisoning cases, according to the map.

Plot of Soil Lead Versus Children's Blood Lead in Detroit - Bickell 2010

Plot of Temporal Variation in Atmospheric Soil and Lead in Detroit - 2001-2009

This plot shows that soil that has been resuspended into the atmosphere is highly correlated with air lead concentrations. This is important as it indicates that air lead levels are linked with surficial soil lead concentrations. Therefore, reducing air lead concentrations must involve isolation of urban lead contaminated soils

Scatterplot with median splines of weather adjusted air lead and air soil in time (daily). Weather-adjusted air Pb and soil estimates (µg/m3) are graphed on the daily time-step, fitting distributions of air Pb and soil values with median splines.

Plot of Temporal Variation in Atmospheric Lead and Children's Blood Lead in Detroit - 2001-2009

This plot shows that children's blood lead levels are highly correlated with atmospheric lead concentrations (which are correlated with atmospheric soil on the previous page). This is important as it is apparent that to reduce children's blood lead levels, soil lead contamination must be isolated. Furthermore, this plot indicates that Pb paint is not thought to be attributable to seasonal variations in children's blood lead levels.

In Flint, Michigan (USA), a public health crisis resulted from the switching of the water supply from treated Lake Huron water to untreated corrosive water sourced from the Flint River in April 2014, which caused lead to leach from water lines exposing a portion of the children in the city. The quarterly blood lead levels of children <6 years old in Flint (as well as in the State of Michigan and Genesee County) were compiled between 2010 and 2015 and the percentage of children with blood lead levels ≥5 µg/dL were calculated by the Michigan Department of Environmental Quality (MDEQ). The percentage of children with blood lead levels ≥5 µg/dL in the third quarter of 2013 (before the water source switch) rose from about 3.6% to about 7% in JulySeptember) 2014 (see Figure 2 below). This figure clearly shows the seasonal nature of childrens blood lead pattern between 2010 and 2015 with a peak in the third quarter and a trough in the first or second quarter. The questions that are not being asked is why did childrens blood lead levels display a seasonal blood lead pattern before the introduction of the new water supply in Flint; and what are the implications of these seasonal blood lead patterns? Based on our interpretation of blood lead seasonality in urban areas such as Detroit (located approximately 100 km southeast of Flint), we infer that before the change in water supply the blood lead peaks in the third quarters in Flint were being driven by seasonal resuspension of lead dust from contaminated soils into the atmosphere during dry periods. This lead source may have been compounded by contributions from lead leaching from water pipes during the summer. This longer-term view of lead uptake via blood lead levels indicates that the blood lead peaks in the third quarters of 2014 and 2015 may have been driven by a combination of lead from resuspended soil-derived dust and lead newly released from water lines.

1. Emissions from Past Use of Lead in Gasoline
2. Exterior Lead Paint

The Emerging Paradigm About The Cause of Urban Lead Poisoning

The emerging lead poisoning paradigm is that chronic urban lead poisoning is caused by exposure to lead contaminated soil (contaminated from past leaded gasoline emissions and exterior lead paint) that is tracked into the interior of homes by shoes(Hunt et al., 2006)and the feet and fur of family pets and exterior urban soil that is re-suspended into the atmosphere where it penetrates interiors of homes and settles on interior contact surfaces(Layton and Beamer, 2009)(Laidlaw and Filippelli, 2008). Children are also exposed to lead via direct ingestion of soil outdoors. Chronic urban lead poisoning can also be caused by exposure to interior lead paint dust particles during renovation of older homes and flaking of interior lead paint dust particles and lead leaching into tap water from old lead pipes. Sometimes, children are exposed to lead originating from BOTH lead paint particles AND from exterior lead contaminated soil dust. Children are primarily exposed via hand to mouth activity (thumb sucking). Acute lead poisoning is probably caused by ingestion of interior and exterior lead paint that has chipped or via ingestion of a large dose of soil with high lead concentrations.

Several Major Pathways of Pb Exposure

Study of lead in house dust, interior and exterior paint and soil in 575 homes in Los Angele and Sacramento, California (Sutton et al., 1995)

In a study of 575 homes in Sacramento, California (USA) Sutton et al. (1995) stated the following: Continuous variables measured in this survey expected to influence lead levels in house dust include age of housing, lead levels in interior and exterior paint and soil and paint deterioration. Spearman correlation coefficients for lead dust concentration levels and age of housing, interior paint, exterior paint and soil were -0.34, 0.19, 0.29 and 0.35, respectively (p < 0.01 for each). These variables had little ability to explain dust lead loading levels measured. Spearman correlation coefficients for dust lead loading and age of housing, lead levels in interior paint, and soil were -0.20, 0.12, 0.15, and 0.18, respectively (p <0.02). Among these four variables, interior paint lead levels had the weakest association with lead levels measured in dust (ppm or micrograms per meter squared). Interior paint condition was not associated with dust lead levels. There was a statistically significant but small relationship between exterior paint condition and lead dust concentration levels in Sacramento (Spearmen correlation coefficient r = 0.16, p = 0.03) and dust lead loading in Los Angeles (Spearmen correlation coefficient r = 0.015, p = 0.02). Households in Los Angeles reporting interior paint changes in the past year had geometric mean dust lead loading levels twice as high as in households not reporting paint changes ( 47 micrograms per meter squared compared to 23 micrograms per meters squared). No correlation between lead concentration and interior paint changes was demonstrated in either of the two communities tested.

Based upon the table above, it should be easily understood that if the exterior soils are contaminated with Pb, the interior
house dust will be contaminated with Pb as well.

This figure suggests that the simple act of residents removing their shoes before entering their homes can have a major impact on the soil lead concentrations inside homes. Another of the many lines of evidence that lead in soil contributes to indoor lead exposure.

In the maps of soil lead concentration below, note that the California residential soil lead guideline is 80 mg/kg

New Orleans, Louisiana (USA)

This chart shows that the inner city soils of New Orleans are highly contaminated with lead. This bullseye pattern is typical of large cities that used lead in gasoline for many years. Unfortunately, the residents of many inner-city areas in the US are African American and Hispanic.

Soil Pb content and corresponding soil Pb loading of the communities of New Orleans

The figure below is particularly important because it shows the soil Pb content along with the corresponding
soil Pb loading of the communities of New Orleans. The map illustrates the difference between
common measurements of soil Pb and the quantities of Pb on the soil surface that children are likely to
encounter during outdoor play activities. The 2013 standard for dust Pb loading on interior floors
is ~431 µg/m2
(40 µg/ft2
based on U.S. standards). Note that in this figure soil containing the minimum
Pb of 6 µg/g has a Pb loading value of ~430 µg/m2
and that soil containing 400 µg/g, the U.S. HUD,
EPA and CDC standard, has a Pb loading value of ~16,200 µg/m2
. This means that the U.S. EPA soil
Pb standard poses a Pb loading value in outside environments which is over 37 times larger than the Pb
dust standard allowed on floors within home interior environments

The USEPA's soil Pb residential guideline is 400 mg/kg. The first chart shows that as soil lead levels increase, children's blood lead levels increase. The second chart (below) indicates the blood lead response of children's blood lead levels (of various age groups)to an exposure of soil lead of 400 mg/g (based upon Mielke's empirical study). This chart indicates that an exposure of 400 mg/kg will result in a blood lead exceeding 5 micrograms per declitre (the current CDC blood lead reference level). Note that lead is not safe at any level.It also shows what the blood lead level response would be using Norways guidelines.
In essence, based upon the current CDC reference level and the empirical soil lead blood blood lead relationship, this chart shows that the 400 mg/kg guideline is inadequate and that it would be appropriate to adopt the Norwegian guideline (note that the California guideline is 80 mg/kg). However this has major implications given the large regions in urban areas exceeding 100 mg/kg.

Syracuse, New York

Indianapolis, Indiana (USA)

Based upon a sample of only 8% of children

Chicago, Illinois

Unfortunately, the African-American and Hispanic populations have the highest exposure in Chicago. This situation appears to be happening in many of the major inner-cities of the USA. The exposure results from a combination of lead in soil dust, flaking lead paint dust and lead water lines. The absence of any efforts to investigate, remediate or educate the public regarding the lead in dust soil exposure pathway in areas predominantly comprised predominantly of African Americans and Hispanics brings some to question whether environmental racism is occurring. Some people ask the question whether urgent action would have occured if this situation was present in white suburban areas.

Philadelphia, Pennslyvania : Lead Poisoning Risk Analysis

Oakland, California

Los Angeles, California

Quote from the conclusion of this paper (Wu et al., 2010): "This study found that areas
occupied by majority (population ratio larger than 50%) African
American and Hispanic populations have higher soil lead
concentrations than Non-Hispanic Whites (data not shown). This
finding implies that minority groups in the study area have a
higher potential for exposure to lead from soils. Considering the
higher birth rates in minority populations, especially people of
Hispanic descent, it is likely that lead from soils plays a
greater role in childhood blood lead poisoning in children who
live in these areas". Note that the soil lead concentrations on this map represent the bioavailable portion of the soil which is easily transferred to the bloodstream when ingested or inhaled. The total concentration for these calculations, which are presented on all the other maps on this site, have much higher concentrations.

Soil Lead Blood Lead Dose-Response:All Examples

Dose-Response-USEPA IEUBK Model

Dose Response - Empirical Relationships

Note that the empirical relationship between soil lead and blood lead observed in New Orleans (below) and Detroit (below) displays steeper slopes than the USEPA IEUBK model (above). This could possibly suggest that IEUBK model is under-predicting blood lead levels at lower concentrations.

New Orleans - Soil Lead Blood lead - Empirical Relationship

Dose-Response - Detroit

Plot of Soil Lead Versus Children's Blood Lead in Detroit - Bickell 2010

Lanphear et al. (1998): increasing soil lead concentration from background to 400 micrograms/g was estimated to produce an increase of 11.6% in the percentage of children estimated to have a blood lead level exceeding 10 micrograms/dL.

Texas Dept. of Health (2004): Using large database from El Paso Area, study found an odds ratio 4.5 (1.4, 14.2)for the relationship between a 500 ppm increase in soil lead and blood lead level > 10 ug/dl.

Maisonette (1997): yard soil remediation showed the strongest association with changes in blood lead levels. This variable was found to be a protective factor for elevated blood lead levels in children (odds ratio, 0.28; confidence interval, 0.08-0.92).

In cases of chronic exposure lead often sequesters in the highest concentrations first in the bones/teeth, then in the kidneys.

Lead Concentrations In Bones/teeth Increase With Age

Priest and Frank (1990) reviewed the literature regarding lead in bones and teeth. Priest and Frank (1990) indicated that modern skeletal levels have been claimed to be 1000 times greater those determined in ancient Peruvian skeletons. The levels of lead in bones has been observed to be highest in inner city residents compared to suburban and rural residents. In addition, a linear increase in the logarithm of the bone lead concentration was found with age (r=0.9). At ages 3 to 4, the mean bone lead concentration for urban specimens was 5.55 ppm 4.05 ppm for suburban, and for rural as little as 1.9 ppm, whereas at ages 9 to 10, the means were 13.1, 10 and 6.3 respectively. Teeth in urban children contained five times as much lead as those of rural children. Another study showed urban tooth lead levels twice as high as suburban levels. These findings have been observed internationally. Thus it has been shown that children efficiently absorb lead which is stored in their bones.(Source - Priest, Nicholas D. , and Van de Vyver Frank. 1990. Trace Metals and Fluoride in Bones and Teeth. CRC Press, 400 p).

Lead Stored in Women's Bones Is Episodically Released During Pregnancy Exposing Fetus and Mother to Lead

IF it is assumed that there is causality between lead exposure and violent attacks, what does that say about the culpability of those who were placed in prisons as a result of the lead peak, as well as those inprisoned due to violence in the inner cities? I do not know the answer.

Solution - Remediation Precedent Set in New Orleans, Evansville and Omaha

1.) Method of Mielke et al.(2011) - New Orleans

"The soil emplacement was conducted by first spreading out a bright orange,
water pervious geotextile material to cover the original soil of the play area. The
geotextile layer prevents Pb-safe soil from mixing with the underlying original soil
and acts as a warning layer to anyone digging into soil. Soil was not removed from
the play areas in this project.
The Pb-safe soil was from the Bonnet Carré Spillway, located up-river from New
Orleans (U.S. ACE or Army Corps of Engineers). The alluvial soil, derived from the
sediments of the Mississippi River at the Bonnet Carré Spillway, has a median Pb content
of 5 mg/kg (Mielke et al., 2000). The Bonnet Carré soil was transported to the childcare
center and emplaced on top of the geotextile layer to a depth of at least 15cm(6 inches)."

EPA and Partners Celebrate Reduced Lead Exposure in Children; Blood lead levels in children around Tar Creek site in Okla. greatly reduced.

Children in Tar Creek and Ottawa County, Oklahoma had historically been exposed to high levels of lead from former mining operations, especially around the Tar Creek Superfund site. In 1997, 21.5 percent of children living near Tar Creek showed elevated blood levels, defined as readings above 10 µg/dl (micrograms per deciliter). For the same year, 12.61 percent of children in Ottawa Co., OK, showed elevated levels.
Since then, through EPA, state, and tribal cleanup activities, lead-contaminated soil has been removed from 2,887 residential yards and public properties in the area. With additional funding from EPA, the Ottawa County Health Department has worked to increase community awareness about lead poisoning prevention and the importance of blood lead screening for children. These activities have achieved striking results, with 0 percent of area children showing elevated levels [>10 micrograms per decilitre] in 2013.

Topsoil Slingers

Terraseeding (mix soil and grass seed)

Hydroseeding

Soil Treatment Strategy

I recommend that soil covering efforts first be conducted in areas where there is a high prevalence of lead poisoning and where soil lead levels are high (triage). I would first focus on roadside soils (0-25m)within these areas and then continue until areas with high lead poisoning prevalence are covered (or funds permit).

Estimated Cost of Urban Soil Lead Remediation - New Orleans

In the journal Environmental Science and Technology, Mielke et al. (2006) estimated the cost to remediate the soils in New Orleans. The abstract is presented below:

In New Orleans, LA prior to hurricane Katrina 20−30% of inner-city children had elevated blood Pb levels ≥10 μg/dL and 10 census tracts had a median surface soil level of Pb >1000 mg/kg (2.5 times the U.S. standard). This project tests the feasibility of transporting and grading contaminated properties (n = 25) with 15 cm (6 in.) of clean Mississippi River alluvium from the Bonnet Carré Spillway (BCS) (median soil Pb content 4.7 mg/kg; range 1.7−22.8). The initial median surface soil Pb was 1051 mg/kg (maximum 19 627). After 680 metric tons (750 tons) of clean soil cover was emplaced on 6424 m2 (69 153 ft2), the median surface soil Pb decreased to 6 mg/kg (range 3−18). Interior entrance wipe samples were collected at 10 homes before and after soil treatment and showed a decreasing trend of Pb (p value = 0.048) from a median of 52 μg/ft2 to a median of 36 μg/ft2 (25th and 75th percentiles are 22 and 142 μg/ft2 and 12 and 61 μg/ft2, respectively). Average direct costs for properties with homes were $3,377 ($1.95 per square foot), with a range of $1,910−7,020, vs $2,622 ($0.61 per square foot), with a range of $2,400−3,040 for vacant lots. Approximately 40% (86,000) of properties in New Orleans are in areas of >400 mg Pb/kg soil and estimated direct costs for treatment are between $225.5 and $290.4 million. Annual costs of Pb poisoning in New Orleans are estimated at ∼$76 million in health, education, and societal harm. Urban accumulation of Pb is an international problem; for example, the new Government of Norway established a policy precedence for an isolated soil cleanup program at daycare centers, school playgrounds, and parks to protect children. New Orleans requires a community-wide soil cleanup program because of the extent and quantity of accumulated soil Pb. The post-Katrina benefits of reducing soil Pb are expected to outweigh the foreseeable costs of Pb poisoning to children returning to New Orleans.

Estimated Benefit of National Urban Pb Paint and ?Soil? Lead Remediation - United States

Gould, 2009 estimated that the net benefit of lead hazard control ranges from $181 to $269 billion, resulting in a return of $17$221 for each dollar invested in lead hazard control. Note that the cost benefit by Gould did not include the cost benefit of reductions in autism, preeclampsia, schizophrenia, mental illness and many other diseases associated with lead poisoning. Thus the benefit of lead hazard reduction is likely to be much greater than Gould's estimates.

Recommended Funding Mechanism To Cleanup Urban Soils

Small Gasoline Tax!

Call For Blood Lead Incidence Data Transparency

I strongly suggest that the new Obama government
publish child blood lead incidence maps of the top 50 cities in the U.S
by graphically displaying the location and all the blood lead
concentrations (>5 ug/dl, > 10ug/dl and >20 ug/dl) for the
previous 5 years, and updated yearly (see Detroit Blood Lead Incidence
Map Above).
The percentage of the children sampled should be boldly presented as
well. These maps should be available for all to see on one central
internet site.
The website would be registered with all the major search engines so
that anyone could locate the data.
This data is already available and could easily be put together in a
two month time period by someone experienced in GIS and the internet.
The funding cost would be extremely small.

Call For National Urban Soil Geochemical Risk Mapping Program

I suggest that the Obama administration use the United States
Geological Survey to conduct an urban soil geochemical risk mapping
program in the 50 largest cities in the
United States. I recommend the geochemical mapping methods be adopted fromthe British Geological Survey,
David L Johnson/colleagues at SUNY-ESF or Howard Mielke and colleagues at Tulane/Xavier.
The results should be placed online in one central location for anyone to view.

Number of cases of elevated blood lead levels ≥10 micrograms per decilitre among children aged <5 years, by month in 2012 in the United States (source of data CDC, 2016)

Children's Blood Lead Levels Also Display Strong Seasonal
Variations With Peaks Generally in the Summer or Autumn When Soils Are
Dry and Prone to Resuspension

A conceptual model of child BPb seasonal Pb poisoning is suggested.
Lead from multiple sources has accumulated in soils of urban
environments. The seasonal resuspension of Pb-contaminated soil in
urban atmospheres appears to be controlled by soil moisture and climate
fluctuations. This study
(Laidlaw et al., 2005)indicates that
higher urban atmospheric Pb loading rates are experienced during
periods of low soil moisture and within areas of Pb-contaminated
surface soils. Children and adults living in urban areas where surface
soils are contaminated with Pb may become exposed through indoor and
outdoor inhalation of Pb dust and ingestion of Pb deposited within
homes and outdoor surfaces. Because resuspension of Pb from
contaminated soil appears to be driving seasonal child BPb
fluctuations, concomitantly, we suggest that Pb-contaminated soil in
and of itself may be the primary driving mechanism of child BPb
poisoning in the urban environment.

Laidlaw et al.'s (2005) model used in the three cities above was independently replicated in Milwaukee, Wisconsin in an unpublished court case

Soil Lead is a Major Source of Atmospheric Lead via Soil Re-suspension

Weather adjusted air Pb and air soil over time, including median spline fits, for Pittsburgh,
Detroit, Chicago and Birmingham.

Weather adjusted air lead versus air soil with linear fit for peak months (June, July, August, and
September) and non peak months (October through May) for Pittsburgh, Detroit, Chicago and Birmingham
combined.

This study also observed..."Atmospheric soil and lead aerosols are 3.15 and 3.12 times higher, respectively, during weekdays than weekends and Federal Government holidays, suggesting that automotive traffic turbulence plays a significant role in re-suspension of contaminated roadside soils and dusts."

Plot of Temporal Variation in Atmospheric Soil and Lead in Detroit - 2001-2009

Scatterplot with median splines of weather adjusted air lead and air soil in time (daily). Weather-adjusted air Pb and soil estimates (µg/m3) are graphed on the daily time-step, fitting distributions of air Pb and soil values with median splines.

I suggest that when the soil is resuspended, the fine fraction where the bulk of the petrol lead particles reside is suspended in the air. This fraction has a higher concentration than the bulk soil and also has a different isotopic signature (more anthropogenic) than the bulk soil. It is also suggested that air lead concentrations can result in very high concentrations at a height of two (m) in the summertime in cities where the soil lead concentrations are an order of magnitude higher than this Mexican city. It does not take much imagination to understand that air lead concentrations at two metres are at the same height as windows which likely results in air lead penetration into homes.

Despite the dramatic decrease in airborne lead over the past three
decades, there are calls for regulatory limits on this potent pediatric
neurotoxin lower even than the new (2008) US Environmental Protection
Agency standard. To achieve further decreases in airborne lead, what
sources would need to be decreased and what costs would ensue? Our aim
was to identify and, if possible, quantify the major species
(compounds) of lead in recent ambient airborne particulate matter
collected in El Paso, TX, USA.

Methodology/Principal Findings:
We used synchrotron-based XAFS (x-ray absorption fine structure) to
identify and quantify the major Pb species. XAFS provides
molecular-level structural information about a specific element in a
bulk sample. Pb-humate is the dominant form of lead in contemporary El
Paso air. Pb-humate is a stable, sorbed complex produced exclusively in
the humus fraction of Pb-contaminated soils; it also is the major lead
species in El Paso soils. Thus such soil must be the dominant source,
and its resuspension into the air, the transfer process, providing lead
particles to the local air.

Conclusions/Significance:
Current industrial and commercial activity apparently is not a major
source of airborne lead in El Paso, and presumably other locales that
have eliminated such traditional sources as leaded gasoline. Instead,
local contaminated soil, legacy of earlier anthropogenic Pb releases,
serves as a long-term reservoir that gradually leaks particulate lead
to the atmosphere. Given the difficulty and expense of large-scale soil
remediation or removal, fugitive soil likely constrains a lower limit
for airborne lead levels in many urban settings.

Urban Atmospheric Lead Is Associated with Particulate Matter Less Than 10 micron in Size (PM10)

Chicago, Illinois

Syracuse, New York

Lansing, Michigan

Children's Blood Lead Seasonality - State of Michigan: 1999-2012.

Milwaukee,Wisconsin (USA)-New

Milwaukee,Wisconsin (USA)-Old

USEPA Discussion - p. 45 "Exposure may increase
in the summer because of factors that include increased outdoor playing time, more
opening and closing of windows, increased hand-to-mouth activity, and drier leaded dust
that more easily enters homes."

To make matters more complex, water lead levels also display seasonal variation

Washington DC

Montreal

UNTESTED Hypothesis for the declines in blood lead levels Following the elimination of lead in gasoline

I have questioned whether the decline if in blood levels following the elimination of lead in gasoline has resulted because in urban areas highly contaminated soils have been resuspended year after year. What could be happening is that a sizable percentage of the resuspended soil and lead falls on impervious surfaces such as roofs and roadways. This material could have then been brought out of the system depositing into sediments in rivers and estuaries. This could conceivably be reducing the lead concentrations in urban soils and subsequents exposures in the atmosphere through resuspension. The "signal" should be present in the sediments of estuaries. (indeed it is in Sydney, AUstralia - see Birch - University of Sydney). This is only a hypothesis at present.

Homegrown Vegetables Are Another Exposure Pathway to Lead in Urban Soil

The recent movement towards cultivating homegrown vegetables, partly
due to the global financial crisis, poses risks due to the uptake of
lead in certain vegetables.

New York City - Garden Soil Lead (median concentrations)

New York City - Association between Blood Lead in Pigeons and Children's Blood Lead Levels

Global Lead Production (million tonnes)

Lead is nefarious element - it is used in bombs and bullets in wars, bullets in crime and poisons hundreds of millions of children and adults worldwide through soil lead and lead paint exposure. Lead also poisons very large numbers of wildlife due to the current and past use of lead shot and bullets.